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Properties of Orbital Angular Momentum (OAM) Waves with Respect to Wireless Communication in Complex Environments and to Electromagnetic Interference

Applicant Professor Dr. Christian Schuster, since 8/2020
Subject Area Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
Term from 2020 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 432301241
 
Final Report Year 2023

Final Report Abstract

Electromagnetic (EM) waves have a multitude of useful properties such as linear and spin angular momentum. In the past years, so called orbital angular momentum (OAM) carrying waves have been introduced to high frequency (HF) engineering as a novel method for signal modulation in wireless communication. This project explored fundamental questions with regard to OAM wave generation, propagation, and reception both from a more physical viewpoint (e.g. reflection, shielding, superposition, and interference) as well as an HF engineering viewpoint (e.g. antenna design, impedance matching, mode conversion, and behavior in complex environments). The goals achieved in this project – mostly by numerical simulations using the Method of Moments – include an improvement of the understanding of the fundamental electromagnetic properties of OAM waves, the generation of guidelines for OAM antenna array design, and the evaluation of OAM based communication in complex environments and subject to electromagnetic interference. Specifically, the following results and insights could be obtained: When uniform circular arrays (UCA) are used, it was found that mode conversion occurs if the environment around one array and between two arrays is not cyclic symmetric. For a single array, that means the used array elements, the orientation of the elements, and the form of the array have to be chosen such that the array ‘looks the same’ from the point of view of every antenna element. The environment between two communicating arrays underlies the same symmetry requirement, and the arrays must be aligned. Examples of cyclic symmetric environments are free space and a cylindrical waveguide. Examples of non-cyclic symmetric environments are communication over the ground and communication in a rectangular corridor. The signal strength of different transmitted OAM modes falls faster over distance for higher OAM modes. It was found that the orientation of the array element can modify how fast the different modes fall off with distance. The OAM modes were found to be able to penetrate apertures of different shapes and sizes. How well an OAM mode penetrates an aperture depends on the aperture size and shape as well as the mode. The problem of interference, where an array receives interfering signals in addition to the actual signal, is found to be particularly problematic in OAM-based communications. This interference can accrue with a third antenna or a reflection from, for example, the ground. The special challenge for OAM antennas is that the transmission of a high mode can fall off faster than the interfering signal and thus leads to a decrease of the signal to interference ratio over distance. Finally, it was found that OAM modes can be applied to transmission lines or waveguides, where no mode conversion arises if the symmetry requirements are met. This can be used in HF-components, for example, as antenna feeds.

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